ACS Photon. (2015)

Hyunsoo Kwon and Sunghwan Kim from Ajou Univesity, Korea, have fabricated biocompatible, tunable colour filters by sandwiching a thin layer of silk protein between two silver films. When illuminated from behind with white light the structure initially has a green appearance associated with a narrowband transmission resonance, but on contact with liquid, the silk layer swells and the reflection redshifts to longer wavelengths. Similar Fabry–Perot-type structures have been used as colour filters before but what makes the silk protein interesting is its strong interaction with its environment. For example, when water and acetone are introduced in varying proportions, the physical volume, or swelling, of the material can be tailored; redshifts as big as 150 nm were observed. The team also etched patterns into the silk spacer using UV light, enabling the creation of different colours in different regions.